Additive manufacturing is a process by which three-dimensional objects may be manufactured from a powder or liquid base. Examples of additive manufacturing processes include stereolithography, selective laser sintering (SLS), direct metal laser sintering (DMLS), electron beam melting (EBM), and laser powder deposition (LPD). Each of these methods may be used to create objects which are not possible to make using subtractive manufacturing or machining.
Stereolithography is the process of filling a chamber with photosensitive liquid in layers. As each layer is filled, a light source hardens thin layers or slices of the desired three-dimensional object. When the desired object has been built up in a layerwise fashion, the unused photosensitive liquid is removed.
SLS is a similar process to stereolithography, but with a powder base rather than a photosensitive liquid. For example, SLS may use a powdered polymer, or a polymer/metal blend. Furthermore, SLS uses a laser, often a CO2 laser, to sinter or melt the powder. SLS is often used to create so-called “green bodies” for use in subsequent molding.
DMLS, like SLS, uses a powder base. However, DMLS uses only metal powders. A single metal or a blend of metals may be used. DMLS also uses a laser as a sintering or melting source. Once a three-dimensional object has been created using DMLS, residual powder is removed. Often, there is enough oxidized, contaminated powder in the residual powder that it is unusable for future additive manufacturing.
EBM is similar to DMLS, but rather than using a laser beam an electron beam is used for heating the target powder. As with DMLS, unsintered residual powder may be too oxidized for use in future additive manufacturing.
LPD uses a laser head to deposit powder only in those regions where it is to be melted. Thus, where other additive manufacturing techniques may have layers or slices of any geometry, each layer or slice in an LPD design must be supported by a sintered layer beneath it. Thus, LPD leaves fewer design options, but results in less contaminated powder.
Each of the foregoing additive manufacturing techniques may be used to create complex three-dimensional structures that cannot be made using subtractive manufacturing (e.g. machining). However, these techniques either suffer from their own design limitations (as with LPD) or from large quantities of waste material (as with DMLS, SLS, stereolithography, or EBM).